1. Field of the Invention
The present invention relates to a novel protein which induces the interferon-.gamma. (hereinafter abbreviated as "IFN-.gamma.") production by immunocompetent cells.
2. Description of the Prior Art
It is known that IFN-.gamma. is a protein which has antiviral-, antioncotic- and immunoregulatory-activities and is produced by immunocompetent cells that are stimulated with antigens or mitogens. Because of these biological activities, IFN-.gamma. has been expected for use as an antitumor agent since it was discovered, and studied energetically on clinical trials as a therapeutic agent for malignant tumors in general including brain tumors. IFN-.gamma. preparations commercially available now are roughly classified into two groups, i.e. one group of natural IFN-.gamma.s produced by immunocompetent cells and another group of recombinant IFN-.gamma.s produced by transformants obtained by introducing DNAs which encode natural IFN-.gamma.s into microorganisms of the species Escherichia coli. In the above clinical trials, one of these two groups of IFN-.gamma.s is administered to patients as an "exogenous IFN-.gamma.".
Among these IFN-.gamma.s, natural IFN-.gamma.s are usually produced by culturing established immunocompetent cell lines in nutrient culture media admixed with IFN-.gamma. inducers to produce IFN-.gamma.s, and purifying the produced IFN-.gamma.s from the resulting cultures. It is known that IFN-.gamma. inducers greatly influences on the IFN-.gamma. yield, the facility of IFN-.gamma. purification, and the safety of final IFN-.gamma. preparations. Generally, mitogens such as concanavalin A (Con A), lentil lectin, pokeweed lectin, endotoxin and lipopolysaccharides can be used as IFN-.gamma. inducers. However, these mitogens have the following problems: (i) their molecules and qualities vary and change depending on their origins and purification methods, and (ii) preparations with a constant IFN-.gamma. inducibility are not readily prepared in a satisfactory yield. In addition, most of these mitogens might induce unfavorable side effects when administered to living bodies, and some of them might cause toxicity, so that it is substantially difficult to induce IFN-.gamma. production by directly administering IFN-.gamma. inducers to the living bodies.